1. Field of the Invention
The present invention relates to a device for purging gas and, more particularly, to a device for purging gas from a conduit.
2. Description of the Related Art
When welding conduit sections of certain materials, such as stainless steel and/or other alloys, for example, it is desirable to remove reactive gases from the weld region. Gases, such as oxygen, tend to chemically react with the molten conduit material and degrade the quality of the resultant weld. Conduit purging systems are used to fill the conduit with an inert gas, such as argon, for example, to displace the reactive gases from the weld region.
Manufacturers of welding systems typically provide specifications identifying recommended purge gas flow rates and pressures to obtain high quality welds for conduits of various sizes and materials. The recommended flow rates and pressures, however, are designated for open-ended conduit sections in which these parameters can be maintained. For open-ended conduits, the purge gas flows through the conduit sections and is either vented or recaptured. A problem arises when welding an open-ended conduit to a conduit having a closed end, such as a cap or a pressure vessel. In such a closed-ended system the purge gas has an inlet, but no outlet. Accordingly, when the gas is supplied to the conduit, the gas pressure within the conduit continually increases until the weld bead blows out of the weld region.
One proposed solution to the problem of welding closed-ended conduits is to turn off the gas purge partway through the welding process, in particular, before the pressure causes weld failure. This solution, however, is difficult to implement, generates uncontrolled purge gas pressure within the conduit, and provides inconsistent results and many failed welds.